Pro Tip

Hidden Triple: three digits each appearing in only three cells within a group — eliminate all other candidates from those three cells.

Pro Tip
✓ Completed! 👍
7
5
6
1
8
1
9
7
1
9
7
6
4
1
8
9
3
5
8
4
1
8
9
8
7
3
6
9
8
4
7
Math Insight

Solving Sudoku is NP-complete for an n×n grid. For the standard 9×9, it's fast — but larger grids become exponentially harder.

Math Insight